1. Field of the Invention
This invention relates to a novel lens barrel for a camera. More particularly, this invention relates to a lens barrel for a camera which includes an electromagnetic driving means for moving a movable lens and a position detecting means for detecting a position of the movable lens. This invention provides a novel lens barrel for a camera wherein an outer shell can be made small in size and configured such that it is free from a partial radial protrusion from the lens barrel by providing a specific arrangement of the driving means and/or the position detecting means. The arrangement does not provide, when the movable lens is moved, such a moment that will cause an inclination of an optical axis of the movable lens.
2. Description of the Prior Art
A lens barrel for a camera having an automatic focusing function or an electrically driven zooming function includes a driving means for driving a movable lens for focusing, or another movable lens for zooming to move in a direction of an optical axis of the lens. Such driving means frequently employs an electromagnetically-driven actuator which includes a coil and a magnet.
An exemplary conventional lens barrel which includes such an actuator as described above is disclosed, for example, in Japanese Patent Laid-Open Application No. 1-196011 and is shown in FIG. 8. Referring to FIG. 8, the conventional lens barrel generally denoted at 50 includes an outer shell 51 having a substantially cylindrical profile. The outer shell 51 has a master lens 52 and some other required lenses (not shown) disposed in the inside of the shell such that the lenses have a common optical axis. The master lens 52 is held on a substantially cylindrical lens holding portion 54 of a lens holding member 53.
The lens holding member 53 is moved by an actuator 55. The actuator 55 includes a housing 56 which is mounted on an outer periphery of the outer shell 51 such that most of the actuator is projected sidewardly from the outer shell 51 and an inner space defined by the actuator 55 is defined contiguously with an inner space of the outer shell 51. A sliding shaft 57 is supported at its opposite end portions thereof for sliding movement by means of a pair of bearings 58 secured to the opposite front and rear end portions of the housing 56 and extends in a direction parallel to the optical axis of the master lens 52. A yoke 60 is secured to the housing 56 and has a disk portion 61, a cylindrical portion 62 which extends rearwardly from an outer circumferential edge of the disk portion 61, and a magnet 63 having a substantially ring-like profile is mounted on a rear face of the disk portion 61 of the yoke 60 in a coaxial relationship with the cylindrical portion 62. The yoke 60 is secured at its disk portion 61 to the housing 56 such that the magnet 63 and the cylindrical portion 62 of the yoke 60 surround a portion adjacent the front end of the sliding shaft 52. A coil bobbin 65 having a hub portion 66 and a coaxial cylindrical coil winding portion 68 is secured at the hub portion 66 thereof in an outwardly fitted condition to the sliding shaft 56. A coil 69 is wound on an outer periphery of the coil mounting portion 68 of the coil bobbin 65 and is positioned corresponding to a location between the cylindrical portion 62 of the yoke 60 and the magnet 63. The lens holding member 53 is secured, at a connecting portion 71 extending from the lens holding portion 54, to a rear face of the coil bobbin 65, and is supported at an arm 72 of the member 53 for sliding movement on a guide shaft 73 secured to the outer shell 51.
Thus, if a driving electric current is supplied to the coil 69, a moving force is exerted on the sliding shaft 57 in accordance with a direction of flow of the driving electric current. Consequently, the coil bobbin 65, the sliding shaft 57 and the lens holding member 53 are integrally moved forwardly or rearwardly (leftwardly or rightwardly in FIG. 8) thereby to move the master lens 52.
With a lens barrel 50 as described above, since the actuator 55 for moving the master lens 52 is positioned such that it projects radially sidewardly from the outer periphery of the outer shell 51, i.e., toward the top of FIG. 8, the outer profile of the lens barrel 50 will have a partial but significant protrusion caused by the actuator 55. Moreover, since a cover is provided on the actuator 55, the projection of the protrusion is unexpectedly great. Thus, there is a problem in that the dimension of the lens system of the lens barrel 50 in a radial direction is considerably greater in dimension compared with a radial dimension of a maximum diameter of the lens system.
Such a protrusion of the lens barrel 50 as described above adversely affects use of the camera since both holding the camera and operation of various operating members disposed on the outer periphery of the lens barrel are made difficult.
Furthermore, since the moving force produced on the coil 69 is applied to the connecting portion 71 of the lens holding member 53, i.e., the portion which is projected sidewardly from the lens holding portion 54 on which the movable lens 52 is held, movement of the lens holding member 53 produces a moment on the lens holding member. Thus, there is a problem that movement of the lens holding member 53 is made to feel heavier, or that the optical axis of the movable lens 52 is inclined by such moment.